


Can't take the heat, get out of the pillow fort.

by Sonamyluffer101



Category: Undertale (Video Game)
Genre: Animalistic Behavior, Animalistic Sans, Animalistic Sex, Biting, Claim Marks, Cunnilingus, Dom Sans, Domestic, Domestic Fluff, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Established Relationship, F/M, Feral Behavior, Fluff, Fluff and Smut, Growling, Heat Sex, I hate myself, Marks, Maybe a multi chapter?, Monster Heat, Oral Sex, Possessive Sans, Purring, Reader has a job, Sans - Freeform, Sans Heat, Sans has instincts, Sans is basically a dog, Sans is needy, Sans is whiny, Sans kills a rabbit, Smut, Tall Sans, This wasn't suppose to be like this, Vaginal Sex, Whining, blanket fort, clingy sans, feral Sans, fort, instincts, netflix, pillow fort, reader - Freeform, reader is female, sans x reader, smut n fluff, sub Reader
Language: English
Status: Completed
Published: 2017-09-11
Updated: 2017-09-11
Packaged: 2018-12-26 09:59:53
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 1
Words: 4,185
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12056610
Author URL: https://archiveofourown.org/users/Sonamyluffer101/pseuds/Sonamyluffer101
Summary: When you came home today, you weren't expecting to find a giant fort made out of pillows and blankets to be in the middle of your living room.You also weren't expecting to be dragged inside of it as soon as you got closer.♡♡♡This was originally suppose to be domestic fluff, but it turned into a heat fic.That's fine, who doesn't like heat fics?Pillow fort shennanigans.Animalistic Sans in heat. What else is better?Might become a multi-chapter?





	Can't take the heat, get out of the pillow fort.

**Author's Note:**

> This wasnt suppose to be smutty, believe it or not.
> 
> Could become a multi-chapter? Idk.

When you came home today, you weren't expecting to find a giant fort made out of pillows and blankets to be in the middle of your living room.

You also weren't expecting to be dragged inside of it as soon as you got closer.

 

* * *

 

 

You let out a small squeak when you were suddenly pulled in and then landed on a small pile of pillows. You looked up to find your boyfriend laughing at you as he held your arm gently.

“What the hell Sans? When did…. Why?!” you exclaimed, shuffling to sit up. This was a mess! You knew for a fact you would be the one who ended up cleaning it, too!

“isn’t it cool?” he asked you, a look of pride on his face. He was just so cute when he felt accomplished... how could possibly you say no?

You were honestly just dreading have to clean it all up as you looked around. There were fairy lights strung up inside of all the sheets and pillows, giving the dark room a warm glow. You had to admit it was nice, even if it was going to be a pain later on.

You looked back at him, seeing the happy look on his face. You sighed softly and then smiled. It must have been a lot of work.

“Yeah… really cool, babe. What's the occasion?”

He gave you a small, almost sheepish smile and looked over at his laptop. “wanna watch a movie?” he asked, clearly dodging the question. You raised an eyebrow but decided not to push it.

You shrugged. “Sure… just nothing too scary. I don't wanna be up all night with nightmares.”

He nodded and then proceeded to go on to Netflix as you got comfy and snuggled into some of the blankets and pillows.

You had a pretty shitty day, so you had to admit this was pretty nice. Lying in a fort with your boyfriend… it was relaxing if you didn't think about the clean up that would come later.

Sans put on the new Death Note movie before laying down next to you and placing the laptop on his knees. He pulled you against him and you snuggled into his warmth as he hit play.

...he was really warm, actually. Was he okay?

You sighed and ignored it, deciding the heat was comforting. He was fine. Just… a spontaneous fort? That’s really random, so you’re probably worrying for nothing. Just took you by surprise.

 

* * *

 

The movie wasn't very good. Not as bad as all the ratings and reviews made it out to be, but definitely not good…

The only thing that made the movie bearable was the fact that Sans had been snuggling and purring against you the whole movie. He gave you a lot of random kisses and nuzzles during the movie as well. He was being really affectionate all of a sudden, not that you minded, it was just out of no where.

He put the laptop down and pulled you a little closer. He got more comfy in the mess of comforting objects as a sudden thought hit you.

“Hey, where's Papyrus?” you asked. He usually got home before you did, so you were a little confused why he wasn't joining you both in the fort.

Sans nuzzled into your neck a little as he answered. “staying at undyne’s for a few days.”

“Really? Why?” They didn't usually have spontaneous sleepovers during the week. Those were saved for the weekends.

“…cuz. asked him too,” he told you, voice slurred and quiet.

“…You asked Papyrus to leave…? Why?” now that just wasn't like Sans at all.

He looked up and his eyes locked on yours for a few seconds before they wandered over to his phone. “…wanna order a pizza?”

Okay, that’s the second question he's dodged. Something was going on.

You made a move to get up and he whined as he pulled you back to him. “no…. let's just get a pizza and stay in here forever…” his voice was rough and he sounded kind of sick… raspy? You were starting to get kinda concerned.

You managed to pull away, much to Sans’s displeasure, and sat up. You looked down at him as he whined and placed his hand on your knee. “Baby, nobody's lazy enough to stay in a fort forever.”

He gave you a look.

“Okay, maybe you are. But I can't, I have work again tomorrow…” you tell him, watching as his face scrunched up in annoyance.

“no, just stay home tomorrow. we can even sleep in here, i mean it's super comfy and-“

“I can't.”

He whined again. Why was he being so whiny? He's never like this. “you never miss work, just take one vacation day, it won't kill you!”

You sighed and looked over at the clock on his laptop. It was about 5:30 and you were kinda hungry… but that could wait.

“Okay. If you tell me what's going on with you all of a sudden, I'll call in tomorrow. Deal?”

He stiffened a bit and then glanced away from you nervously.

You raised an eyebrow. Him? Nervous? What the hell was going on!?

“just… don't get freaked out, okay?”

Well now you were freaking out internally, but you nodded and waited for him to continue.

He sighed and picked a pillow before smothering his face with it. He mumbled something and you rolled your eyes. “Can't hear you. “

He mumbled again and you giggled a little as you moved to straddle him, resting your hands on his chest. This was something you had done a million times before, so you were a little surprised when he stiffened underneath you, and you could hear his breathing getting quicker.

“Sans, you're starting to freak me out a little,” you admit, moving to get off of him.

His hands quickly shot up and held yours against his chest, giving you the message he didn’t want you to get off. You settled back down on his torso and his hands gradually went up your arms, and down your torso until he was able to hold your hips. Your face flushed as you felt him slide you down a little so you could feel his… oh God. Was now really the time to be turned on, Sans?

“Sans, wha… what's going on?” you asked as you tried to shift away, but he held you there and let out a small whimper.

You took the pillow off of his face and saw how flushed his face was. Was he sick? Did he have a fever?

You put the back of your hand to his forehead and were immediately alarmed by how hot he was. He was definitely burning up!

You ripped your hand away and met his gaze. He looked so… out of it. Like he was in a daze. “i’m fine, baby,” he assured you softly.

“No, you're not! You're burning up! Do you have a fever? Is that why you made Papyrus leave, cuz you didn't want him to worry? It's okay to ask for help Sans,” you start to ramble, and he brings one hand up to cover your mouth.

“it's okay. ‘m not sick,” he assured you again.

Okay, now you were just confused. If he wasn't sick, then why was he so warm? “Then, what is it?”

He looked away from you and you sighed before trying to get up again. He let out a tiny growl and held you firmly in place. “no… please, just… gimme a second to think of how to word this…”

You shifted a little to get comfy as you waited, trying to ignore his obvious _bone_ r. A few moments went by with him awkwardly staring at the entrance of the fort and thinking.

“i just…” he finally started, “i don't wanna freak you out…”

“You're not gonna freak me out. Just… talk to me. It's just me, babe.”

He looked at you for a couple of seconds and then it looked like the idea hit him.

“oh! okay, so, you know how you get those period things?”

You felt your face heat up as you nodded. You had to explain menstrual cycles to him the day he found a little bit of blood on the sheets and freaked out because he thought you were hurt. You almost shuddered at the memory.

“I swear to God Sans, if you tell me you get a ‘Monster Period’, I’m gonna slap you.”

He snorted and shook his head. “no. no monster periods. pretty sure yours are ‘ _monstrous_ ’ enough.” You glared at him and he smiled proudly.

“Okay… Then, what is it?”

His smile fell and he averted your eyes again for a moment. “...can i have a kiss?”

You were a little surprised by the sudden request, but you didn’t reject.

You leaned down and kissed him gently, enjoying the way one of his hands left your hip and tangled into your hair.

You squealed softly against him as you were suddenly flipped underneath him. He had your hands pinned on either side of your head and he was kissing you pretty roughly. This was new, but definitely not unwanted. You felt him grind down against you gently and you lost your breath for a second. You could hear a small rumbling in the back of his throat… almost like a growl?

“S-Sans, what.... What is going on? Please, please tell me?” you asked as you managed to gently push him back. He stared down at you with a conflicted look on his face.

He takes a deep breath and looks away before finally speaking.

“...i’m in heat.”

“...Huh?”

Heat? Like… a dog?

He groaned and leaned down so he was hiding his face in your shoulder.

“Heat..? Like a dog?”

He groaned again and hugged your body. “no... yes? i... i don’t know, baby… just… yeah. like a dog, i guess.”

“Okay… so what are the differences?”

“...i guess for monsters it’s different because it only really happens if i have intense feeling for someone.”

You almost smiled. “Oh yeah? You have intense feelings for me?”

You yelped softly when you suddenly felt him bite down on your neck. “hush,” he muttered softly as he licked the mark.

You groaned and tried to push him off, but he whined and held onto you tightly. “no, don't push me away!”

You sighed and let your hands rest at your sides. Was he gonna be whiny the whole time? Wait… how long did this last?

“Babe?”

He made a small grunt of acknowledgement and licked your neck again. You shuddered and held onto the sides of his jacket, your elbows still resting on the ground.

“H-How… how long does this last?”

“…three to five days… maybe a week?”

You nodded slowly and made another move to get him off. He whined again and held on tighter.

“C’mon Sans, I gotta eat and go to bed! I have work in the morning!” you complained, letting your hands flop down dramatically.

He lifted himself quickly and gave you a hurt look. “you said if i told you, then you'd call in!”

You blinked twice and realized you did say that… shit. “…Okay… but why?”

He blushed and glanced down at your body for a second before lowering himself to kiss your neck again. You felt his hands land on your hips and then slide their way into and up your shirt. You whimpered as he touched the sensitive skin underneath your chest, and then it hit you.

He's in heat idiot! He's not just gonna be whiny, he's gonna wanna pound you into a mattress!

Or very comfortable pillow fort.

“Babe, that… we… _fuck_ , yeah… I can't stay out of work for 5 days…”

“it's almost the weekend. you're fine.”

You whined as he started to unbutton your shirt. “W-Wait! I’m stIll hungry…” you complained, giving a tiny pout.

He quickly shot up. “you're hungry? what do you want, princess?”

…Well that was kinda weird.

“…I dunno. Anything really, I just want some food.”

You blinked and suddenly he was gone.

“…Sans?” you called out.

“yup, just hold on. i’ll be right back,” you heard him calling from what sounded like towards the door.

You heard a small pop and suddenly, you knew you were alone. Where was he going!? You went grocery shopping yesterday! There was plenty of food in the house. You whined and laid back down on the blankets before putting on another movie on his laptop. Might as well do something while you wait for him.

 

* * *

 

 

 

You fell asleep. When you woke up, he still wasn’t back.

The clock on his laptop told you it had only been about 40 minutes, but you were still worried. Also, you had to pee.

You crawled out of the fort and went upstairs to use the bathroom. When you came back down, Sans was just coming in, but he was holding something behind his back.

“Uh… hi? Where did you go?”

“...why are you out of the den?”

Den? What?

“Um… I had to pee?”

“get back in the den.”

You frowned. “No, tell me what you have behind your back.”

He growled softly. **“g e t i n t h e d e n.”**

You blinked twice and then sighed, deciding it was better to not argue. “Okay, fine… if you tell me what you’re hiding first,” you compromised, walking a little closer to him. His expression softened and he leaned down to kiss your forehead.

He sighed and you almost screamed when he showed you.

A fucking dead rabbit!?

You whimpered and looked back up at him. “Wh.. why!?”

He kissed you gently and then disappeared, and you heard him reappear back in the kitchen. “get in the den.”

“It’s a fort!”

“yep.”

You groaned and crawled back into your comfortable prison, internally screeching. Was he expecting you to eat a bunny!? Why couldn’t he just make you eggs or something!?

“i love you,” you heard him say from the kitchen.

You blushed and sighed. “I love you too.”

You waited for him anxiously, really wishing he would give you Ramen Noodles instead. You knew he wouldn’t, but you could still hope.

But, why!? Why was he acting like this? You get that he’s in heat, but...

Oh, right… his instincts were probably running wild and forcing him to find fresh meat for you. This whole thing was a lot to handle, but you still loved him, so you had to put up with it.

You closed your eyes again, but didn’t feel tired enough to sleep. Also the hunger gnawing at you gut was kind of distracting, too.

You were drifting in and out of sleep for what seemed like hours, when eventually Sans finally came into the fort. He placed a big plate with meat and vegetables down next to you. You wiped the sleep from your eyes and sat up, looking at the plate and then up at him.

“eat.”

“...Can’t we just have Ramen Noodles or something?”

“no. ramen has so much sodium, it’s not healthy.”

You glared lightly. “Are you seriously lecturing me about health?”

He growled softly. “i love you. i need you to be healthy.”

You sighed softly and picked up the plate. The meat looked like it was seasoned, thank God, and properly cooked.

“Why did you kill a bunny?”

“...because.”

You sighed and started to eat the vegetables, which were very good of course. Sans seemed satisfied you were eating and curled up against your side. You finished the veggies and started to poke at the cut up rabbit meat. You had never eaten a bunny before, so you weren’t really sure what to expect when you took a bite.

You were pleasantly surprised by how good it tasted.

“This is really good,” you told him after you finished the first bite.

He gave a small sound of acknowledgement and nuzzled your thigh.

You quickly finished the food while your mind wandered everywhere. Was your boss gonna get pissed at you for calling in tomorrow? What were you gonna do all day? Well, you had a pretty good idea, but still… all day?

“done?”

You looked up at Sans when he suddenly pulled you out of your thoughts. When did he sit up? Had he been staring the whole time?

“..Yeah, thanks it was really good.” He took the plate from you while you were speaking and then disappeared again. You heard the sound of a dish being put in the sink and then suddenly he was back in front of you.

“are you finally mine?” he asked.

You blushed and sighed before nodding and reaching for him.

His face lit up and he quickly pulled you into his lap, nuzzling his face into your neck. He inhaled your scent and you giggled a little at the tickling sensation. This was something he did often, so you weren’t really phased by it.

“i love you so much…”

You whimpered, feeling his tongue suddenly slide across your neck. “I love you too,” you said in a breathy moan.

He slammed you down against a small pile of pillows suddenly, making you whimper in surprise. He leaned back down to your neck and started to kiss and lick it, making your body heat up a bit. He started to unbutton your shirt, but clearly got impatient, because he growled and then just ripped it, causing the buttons to fly off.

You both froze for a second.

He whined before he pulled back and gave you an apologetic look. “...sorry.”

You gulped. “It-It’s okay… Didn’t really like that shirt anyways…”

He watched as you sat up a bit and removed the tattered shirt from your body and then unclipped your bra. As soon as you unclipped it, he grabbed it and tossed it another direction before grabbing your exposed chest. You bit your lip and felt your face heat up.

He leaned down again and kissed right between your breasts before kissing each nipple. You whined softly as he pulled back and started to unbutton your jeans. You could see he was getting frustrated already, so you quickly said “I’ll do it,” since you didn’t wanna lose your pants, too.

He watched impatiently as you unbuttoned and unzipped your jeans and then he quickly slid them down your legs, along with your underwear, before tossing them in the same direction of your bra.

He pulled back for a second to look at you before a small whine erupted from his throat. You were just so beautiful. He leaned down and kissed your stomach before making his way down. You swallowed hard as you watched him go lower, knowing what he wanted to do.

He was in between your thighs and you felt your heart racing. It wasn’t the first time he had done this or anything, it just… feels a lot more intimate right now for some reason. He kissed your right thigh and then the left one, before going to back to your right thigh and then biting down. You yelped softly and covered your face. That should’ve been painful, but it was strangely arousing.

He pulled away and then licked the bite gently, making you shudder. He chuckled and then finally, finally, he licked you.

You mewled and felt your toes curl as you subconsciously tried to get closer to him. He was licking your clit roughly, and it was so good. Today had been so fucking stressful, so this was more than amazing for you. You made a small sound and he started to purr, causing a tiny vibration on his tongue.

He whined as he licked you, clearly enjoying your taste, and also clearly very turned on.

“Holy shit,” you moaned breathlessly, covering your face. He growled and grabbed your arms, pinning them down to your sides. He stared at you as he ate you out and it was extremely intimate. You bit your lip and looked up at the ceiling, not being able to meet his gaze.

You were whining and moaning as his tongue swiped your clit over and over, causing heat to build up in your stomach. You felt so fucking good!

 

But then he stopped.

 

You whined loudly and tried to grind back down on his tongue, but he kissed you one last time before moving to hover over you.

“sorry baby… i’m impatient,” he muttered as he started to pull his pants down. He kept them on, but he pulled his dick out. You let out a shaky breath as he positioned himself quickly.

“i love you,” he muttered as he kissed your forehead gently.

“I love yo- _Ahh!”_ you started, but had to cut it off with a moan as he started to push in. You clung to the front of his jacket and hid your face in his chest. You weren't very good with intimacy.

He moaned loudly as he slid in, clutching your hips and leaving gentle kisses on your head. “god… you have no idea how much of a relief this is, babe…”

You did, actually. It had been a while since you last had sex so it really did feel like a relief. You whined in response and he chuckled, followed by a low growl as he started to thrust rhythmically. You let out a breathy moan as you let your head flop back down on the pillows, which in turn allowed him to lean down and kiss your chest.

He licked between your chest, making his way up to your neck, causing you to mewl and shudder. “P-Please!” you exclaimed, now trying to get his jacket off. You needed more of him.

He could feel your desperation, and it was making him anxious now. He whined and quickly ripped it off of himself. It was almost as if it was physically burning his bones, and he knew your skin was the only thing that could cool him down. You hugged him close to you, feeling his rib cage against your chest. One of his ribs were brushing against your nipple, which was very pleasurable in your arousal.

He sped up his thrusting as he clutched your body to his, refusing to let go in his animalistic state. “mine…”

You moaned at the sudden possessiveness, feeling his tight grip on your skin. “Yours!” you assured him. He growled, your words only seeming to egg him on further. He started pounding into you faster and faster, and you were starting to see stars. You were still so sensitive from his tongue, and you were close! You were so close!

He could feel it. He could feel you getter wetter and wetter, and closer to orgasm. He reached his hand down and started to rub circles into your button, making your legs twitch and your breath hitch. He licked your cheek gently, speeding up again somehow.

You screamed as you came, the intense feeling of your orgasm washing over you. “F-Fuck…” you whined, feeling sensitive as he pulled his fingers away but kept thrusting. He was swelling, and you knew he was close as well.

“fuck… i’m cumming… i’m cumming, baby girl,” he growled and then bit down on your left shoulder. You cried out as you felt him cum inside you, pain and pleasure both washing over you.

After a couple of seconds he released the bite and then licked it lovingly. “shit… you're amazing.”

You moaned in response, exhaustion suddenly washing over you. He left a gentle kiss on your forehead and then nuzzled into your neck. You were tired, and he was kind of heavy…

“Get up,” you whined softly, trying to push him off.

“can’t.”

“…What do you mean you can't?”

He snorted. “can you _knot_ feel that or something?”

Your face scrunched up in confusion. “What?”

“i’m _knot_ gonna be able to get up for a little while, baby.”

Realization hit you like a ton of bricks. He knotted you. Right. Heat. How did you not realize before? It was practically pulsing.

You sighed and stared up at the top of the fort. Oh well… it was kinda cozy?

He pulled away from your neck and looked at you. You looked back at him and he gently kissed you before running his tongue over your lips. You giggled a little and he smiled, moving his face to lick your cheek.

You groaned at that and tried to wipe it away, but he frowned and licked it again, before starting to lick rhythmically. You sighed and closed your eyes, frowning as you gave up and let him do whatever this was. He started purring, and that slowly put a small smile on your face. You had to admit that was cute.

He started to lick your hairline, and you stared up at him as he did so. He had his eye sockets closed and was still purring. “…Sans?”

“hmm?”

“…Watcha doin’?”

He froze. “…i don't actually know.”

You snorted. This was gonna be a long week, wasn't it?

**Author's Note:**

> Be my friend on Tumblr! I do headcanons! https://www.tumblr.com/blog/skelesansation


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